Week 7 Flashcards
Key information about smooth muscle
Cells form layers and line the cavities of hollow organs
Contractions are controlled by the autonomic nervous system
Cells are connected to eath other electrically and mechanically
How are smooth muscles arranged
What does this arrangement allow them to do
Smooth muscles have no sarcomere.
The actin and mysoin filaments are arranged in the form of a lattice around the cell, allowing the smooth muscle to change shape
Dense bodies
Actin filaments attach to the cell via specialised areas in the cytoplasm called the dense bodies
Dense bands
Smooth muscle cells are mechanically connected to neighbouring cells via specialised areas on the membrane called dense bands
How are smooth muscles activated
There are no neuromuscular junctions
The neurotransmitter is released from varicosities
Difference between the activation of a single unit smooth muscle and a multi unit smooth muscle
Single unit - cells are electrically coupled by gap junctions and function as a unit
Multi-unit - cells are not electrically coupked
Each cell needs to be activated by a nerve
How can smooth muscle be activated
Rhythmically by pacemaker potentials or by acute events that pushes the balance of excitation and inhibition above threshold
No sarcomere arrangement means that
Myosin and actin can slide past each other without entering the end of a sarcomere
Role of calcium in smooth muscle
No troponin in smooth muscle so actin binding sites always available
Calcium source is from the sarcoplasmic reticulum or extracelluar sources which activates calmodulin, which activates myosin light chain kinase
Calcium acts on ______________ as opposed to _____________
Thick filaments as opposed to thin filaments
Relaxation of smooth muscle
Happens by myosin light chain phosphatase
If it overwhelms the activation of muscle due to not enough calcium then the muscle will relax and vice versa
What is cardiac output
What is the abbreviation
What are the units
How is it calculated
Cardiac output is the volume of blood pumped out by the heart every minute
Q
ml or l so the units are ml/min or l/min
Heart rate x stroke volume
What happens to CO, HR and SV when workload increases
HR has a linear relationship
SV decreases with more workload as heart has less time to refill
This pushes cardiac output down as workload increases
How does the parasympathetic system slow heart rate
Parasympathetic nerve endings (vagus nerve) secretes the neurotransmitter acetylcholine
How does the sympathetic system increases heart rate
Sympathetic fibres (cardiac nerves) supply the SA and AV nodes and increase HR by releasing norepinephrine
Stroke volume is regulated by two opposing factors
The force by which the muscle cells contract
The arterial pressure against which they have to eject the blood
The force of contraction is regulated by two processes
The length-tension properties of cardiac muscle cells and the effects of hormonal influence on the contractility of cardiac muscle
Starlings law
Increases in venous return
Greater diastolic filling of the heart
Increased chamber elasticity
Increased ejection fraction
Increased force of contraction
Increased stroke volume
To have an increase in cardiac output, what is required
Increase in HR
Increase in SV
For heart rate to increase, what has to happen
Vagus nerve activity decreases
Sympathetic nerve activity to increase
Circulatory epinephrine increases
For stroke volume to increase, what needs to happen
End diastolic volume to increase
Circulating epinephrine increases
Sympathetic nerve activity to increase
What is blood pressure
Driving force for flow in the cardiovascular system
What must blood pressure be?
It must be regulated, so that it is high enough to create flow, but not too high to put excessive stress on the cardiovascular system
Equipment used to measure blood pressure
Inflatable cuff
Pressure gauge
Stethoscope
When the cuff pressure is below diastolic pressure
Blood flows freely and there is no sound
When the cuff pressure is above systolic pressure (>120mm Hg)
There is no blood flow and no sound as you have collapsed the arteries
As you slowly lower the cuff pressure to between systolic and diastolic pressure (80-120 mm Hg)
There is intermittent flow and tapping sounds
As you lower the pressure further to below diastolic pressure
You loose the sound, telling you the diastolic blood pressure
How is mean arterial pressure calculated
Mean arterial pressure is calculated from the values of systolic and diastolic blood pressure, but it is not an average of the two
Diastole lasts almost twice as long as systole therefore MAP is weighted more heavily towards the diastolic blood pressure value
How to calculate MAP
MAP = diastolic + (systolic-diastolic / 3)
Normal blood pressure values, and mean arterial pressure
Normal blood pressure for systolic is 120 mmHg, 80 mmHg for diastolic and 93 mmHg for mean arterial pressure
Why does blood pressure increase with age
Arteries become stiffer with age due to loss of elasticity
Arteries less able to expand and due to blood supply being the same, blood pressure increases with age
On average, women have ______ blood pressure than men throughout their lives
Lower
Pressure is higher in the foot and lower in the head due to
Hydrostatic pressure
In dynamic exercise, mean blood pressure remains relatively steady
Why?
There is an increase in systolic pressure (demand for blood rises) but also a reduction in diastolic pressure - due to arteries being more relaxing and welcoming of blood
Conversely, in static exercise (lifting weights) mean blood pressure rises dramatically
Yep
Role of the adevntitia
Provides structural strength and tethers the vessels in place
In large vessels, the adventitia is so large, it has its own blood supply
Elastin
Give vessels mechanical strength and their elastic properties (expand and recoil)
Endothelium
The endothelial layer is the filtering interface between the blood and the body
Smooth muscle
Supplies the vessels with contractile power and regulates the diameter of the lumen
Pre capillary sphincter
Controls blood flow to specific capillary beds selectively
Active hyperaemia
The increase in blood flow according to the metabolic needs of the tissue in question
Flow autoregulation
Concerned with the maintenance of blood flow rather than changing it. When the driving pressure drops, the vessels dilate, and when it increases the vessels constrict
Factors that affect arterial diameter
-Neural controls
Neural controls
-vasoconstrictors - sympathetic nerves that release norepinephrine
-vasodilators - neurones that release nitric oxide
Factors that affect arterial diameter
-Hormonal controls
Vasoconstrictors - epinephrine, vasopressin
Vasodilators - epinephrine
Factors that affect arterial diameter
-Local controls
Vasoconstrictors - internal blood pressure
Vasodilators -
Decreased o2
What is special about epinephrine
It can cause vasodilation or vasoconstriction depending on what receptors it binds onto
Fick’s law of diffusion for capillaries
Flow of gas = area/ thickness x D X (P2-P1)
Types of capillary arrangement
Continuous - cells tightly packed
Fenestrated - have tiny openings
Discontinuous - large gaps to allow red blood cells through
2 forces that compete for fluid regulation in a capillary
Hydrostatic pressure forces fluid out of the capillary
Colloid osmotic pressure of proteins within the capillary pulls fluid into the capillary
Net pressure =
Hydrostatic pressure - colloid osmotic pressure
Difference between a vein and an artery
Veins have
Larger diameters
Less elastic tissue
Less smooth muscle
Are more distensible
Thinner walls
Valves
Difference between a healthy vein and a diseased vein
In healthy veins, flow is only towards the heart. Backflow is prevented by shut valves
In a diseased vein, leaky valves allow blood to move in the opposite direction causing blood to accumulate in the extremities
Skeletal muscle pump
Compression of veins by muscle contraction empties them of blood towards the heart
Respiratory pump
Creates a pressure difference between the abdomen and the thoracic cavity that promotes blood return to the heart
